Dual back-plate and diaphragm microphone

ABSTRACT

A MEMS microphone includes a substrate having an opening, a first diaphragm, a first backplate, a second diaphragm, and a backplate. The first diaphragm faces the opening in the substrate. The first backplate includes multiple accommodating-openings and it is spaced apart from the first diaphragm. The second diaphragm joints the first diaphragm together at multiple locations by pillars passing through the accommodating-openings in the first backplate. The first backplate is located between the first diaphragm and the second diaphragm. The second backplate includes at least one vent hole and it is spaced apart from the second diaphragm. The second diaphragm is located between the first backplate and the second backplate.

REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.16/506,037, filed on Jul. 9, 2019, which claims the benefit of U.S.Provisional Application No. 62/737,245, filed on Sep. 27, 2018. Thecontents of the above-referenced patent applications are herebyincorporated by reference in their entirety.

BACKGROUND

A MEMS microphone generally includes a conductive diaphragm and aconductive backplate that is spaced apart from the conductive diaphragm.When the conductive diaphragm is deformed by energy of sound waves, achange of the capacitance between the conductive diaphragm and theconductive backplate can be detected. With the MEMS microphone, soundwaves can be converted to electrical signals by sensing this capacitancechange.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a top view of a diaphragm in a MEMS microphone.

FIG. 1B is a cross-section view showing a MEMS microphone that isfabricated on a substrate.

FIG. 2 is a cross-section view of a MEMS microphone having dualdiaphragms in accordance with some embodiments.

FIG. 3A is a schematic of the first diaphragm as viewed in a plane inaccordance with some embodiments.

FIG. 3B is a schematic of the first backplate as viewed in a plane inaccordance with some embodiments.

FIG. 3C is a schematic of the second diaphragm as viewed in a plane inaccordance with some embodiments.

FIG. 3D is a schematic of the second backplate as viewed in a plane inaccordance with some embodiments.

FIG. 3E is a schematic of the second backplate having an alternativelayout of the vent holes as viewed in a plane in accordance with someembodiments.

FIG. 4 is a cross-section view of a device structure that is anintermediate product created during the process of manufacturing inaccordance with some embodiments.

FIGS. 5A-5D are cross-section views of device structures for showing onemethod of manufacturing a MEMS microphone in accordance with someembodiments.

FIGS. 6A-6D are cross-section views of device structures for showinganother method of manufacturing a MEMS microphone in accordance withsome embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Many micro-electromechanical system (MEMS) devices can be manufacturedusing semiconductor device fabrication methods. Examples of these MEMSdevices include MEMS microphones, such as, a MEMS microphone 90 asillustrated in FIGS. 1A-1B. FIG. 1B is a cross-section view showing aMEMS microphone 90 that is fabricated on a substrate 40. The MEMSmicrophone 90 includes a backplate 60 and a diaphragm 50 spaced apartfrom the backplate 60. Both the backplate 60 and the diaphragm 50 can beelectrically conductive, which form a capacitive element. An electricalcontact 82 electrically connected to the backplate 60 forms a firstterminal for the capacitive element, and an electrical contact 84electrically connected to the diaphragm 50 forms a second terminal forthe capacitive element.

FIG. 1A is a top view of the diaphragm 50 of the MEMS microphone 90 inFIG. 1B. The cross section A-A′ of the diaphragm 50 is illustrated inFIG. 1B. The diaphragm 50 includes multiple venting holes 55 distributedon the diaphragm 50 (e.g., venting holes as shown or more). Thediaphragm 50 also includes one or more anchor areas 58 located near aboundary of the diaphragm 50. The anchor areas 58 allow the boundary ofthe diaphragm 50 to be fixed relative to the backplate 60 and allow gapsbetween the diaphragm and the backplate to be changed at the center ofthe diaphragm 50 and at other locations on the diaphragm at somedistance away from the anchor areas 58. The diaphragm 50 is deformableby energy of sound waves to make the diaphragm 50 bend towards or awayfrom the backplate 60, as the sound waves exert pressures on thediaphragm 50 through an opening 45 in the substrate 40. The backplate 60has multiple open areas 65. There is an air volume space 85 between thediaphragm 50 and the backplate 60. Air can get out of or get into theair volume space 85 through the air passages formed by the open areas 65on the backplate 60 and/or by the venting holes 55 on the diaphragm 50,as the diaphragm 50 bends towards or away from the backplate 60.

The bending movement of the diaphragm 50 relative to the backplate 60caused by the sound waves changes the capacitance of the capacitiveelement between the diaphragm 50 and the backplate 60. Such change ofthe capacitance can be measured with the electrical contact 82 and theelectrical contact 84. For the same amount of air pressure exerted onthe diaphragm 50 by the sound waves, if the rigidity of the diaphragm 50decreases, the amount of the bend of the diaphragm 50 caused by thesound waves increases and the induced change of the capacitanceincreases as well. That is, decreasing the rigidity of the diaphragm 50improves the sensitivity of the MEMS microphone 90. The rigidity of thediaphragm 50 can be decreased by selecting the material for making thediaphragm or by decreasing the thickness (“t” as shown in FIG. 1B) ofthe diaphragm.

The diaphragm 50 in the MEMS microphone 90 generally has to withstand anair blow test. For example, when the air pressure exerted on thediaphragm 50 by the air blow test is at about 0.2 MPa, the chance ofgetting the diaphragm 50 broken should be statistically negligible underaccepted statistical standard. While increasing the rigidity of thediaphragm 50 can decrease the chance of breaking the diaphragm 50, suchincreasing of the rigidity also lowers the sensitivity of the MEMSmicrophone 90. In an alternative method, increasing the size of theventing holes 55 and/or increasing the total number of the venting holes55 to increase overall open ratio can also decrease the chance ofbreaking the diaphragm 50. But such measure of increasing open ratioalso lowers the sensitivity of the MEMS microphone 90, because suchmeasure also lowers the sensing area. Furthermore, increasing open ratiomay also increase the low corner frequency of the MEMS microphone 90,making it less sensitive to low frequency sound waves. It is desirableto improve diaphragm's chance to survive air blow tests without losingthe sensitivity of the MEMS microphone.

Additionally, when particles and/or vapor get into the air volume space85 between the diaphragm 50 and the backplate 60, the physical movementof the diaphragm 50 relative to the backplate 60 can be hindered becauseof stiction effects, which causes sensitivity degradation of the MEMSmicrophone. The stiction effects may also make the MEMS microphoneappear to have unstable and/or inconsistent sensitivity. While methodsof using dimple structure and surface treatment on the diaphragm 50and/or the backplate 60 can be used for reducing the influence of thestiction effects, these methods may still be not effective. Moretechniques may be needed for reducing the influence of the stictioneffects on the performance of the MEMS microphone.

FIG. 2 is a cross-sectional view of a MEMS microphone having dualdiaphragms in accordance with some embodiments. In FIG. 2 , a MEMSmicrophone 100 includes a substrate 40, a first diaphragm 101, a seconddiaphragm 102, a first backplate 111, and a second backplate 112. Insome embodiments, the first diaphragm 101 and the first backplate 111are both conductive and form two conductive terminals of a firstcapacitive element; the second diaphragm 102 and the second backplate112 are both conductive and form two conductive terminals of a secondcapacitive element.

FIG. 3A is a schematic of the first diaphragm 101 as viewed in A-A′plane in accordance with some embodiments. FIG. 3B is a schematic of thefirst backplate 111 as viewed in B-B′ plane in accordance with someembodiments. FIG. 3C is a schematic of the second diaphragm 102 asviewed in C-C′ plane in accordance with some embodiments. FIG. 3D is aschematic of the second backplate 112 as viewed in D-D′ plane inaccordance with some embodiments. The cross-sections of the firstdiaphragm 101, first backplate 111, the second diaphragm 102, and thesecond backplate 112, in the V-V′ plane, are illustrated in FIG. 2 . Thecross-sections of the substrate 40 and other layers of materials arealso illustrated in FIG. 2 .

As shown in FIG. 2 , the substrate 40 includes an opening 45. In someembodiments, the substrate 40 can be a monocrystalline silicon substrateor a semiconductor-on-insulator (SOI) substrate (e.g., silicon oninsulator substrate). For example, the substrate 40 can be silicon,glass, silicon dioxide, aluminum oxide, or a combination thereof. Insome embodiments, CMOS circuit can be fabricated on a silicon substrate.

The first diaphragm 101 faces the opening 45 of the substrate 40. Insome embodiments, a layer of base oxide 70 is formed between thesubstrate 40 and the conducting layer for the first diaphragm 101. Thefirst diaphragm 101, spaced apart from the first backplate 111, isjointed with the first backplate 111 by a first seal structure 141 at afirst boundary enclosing a first empty space 161 between the firstdiaphragm 101 and the first backplate 111. The first backplate 111 hasmultiple accommodating-openings 115 to allow pillars 120 to passthrough. The second diaphragm 102 joints the first diaphragm together atmultiple locations by pillars 120 through the accommodating-openings 115in the first backplate 111. The first backplate 111 is located betweenthe first diaphragm 101 and the second diaphragm 102. It will beappreciated that “empty space” as used herein, does not necessary meanthe space is devoid of all atoms, but rather suggests that the spacecorresponds to vacuum, a fluid, or a gas (e.g., air or nitrogen).

The second diaphragm 102 is jointed with the first backplate 111 by asecond seal structure 142 at a second boundary enclosing a second emptyspace 162 between the second diaphragm 102 and the first backplate 111.The second diaphragm 102, located between the first backplate 111 andthe second backplate 112, is jointed with the second backplate 112 by athird seal structure 143 at a third boundary enclosing a third emptyspace 163 between the second diaphragm 102 and the second backplate 112.The second diaphragm 102 has multiple openings 105 that form airconnections between the second empty space 162 and the third empty space163.

In the embodiments as shown in FIG. 2 , there are multiple chambers 130located at one side of the second backplate 112. In some embodiments,the second backplate 112 has a vent hole 125 that forms an airconnection between the third empty space 163 with an inner space 138 inone of the multiple chambers 130. In some embodiments, the secondbackplate can have more than one vent hole 125 that forms an airconnection between the third empty space 163 with the inner space 138.The chamber 130 includes a side wall 132 spaced apart from the secondbackplate 112. The side wall 132 has two sealable openings 135, and eachof the two sealable openings 135 is laterally shifted from the vent hole125. In some embodiments, the side wall 132 can include only onesealable opening, which is laterally shifted from the vent hole 125. Insome embodiments, the side wall 132 can include more than two sealableopenings each laterally shifted from the vent hole 125. The sealableopenings 135 as shown in FIG. 2 can be sealed with a hermeticsealing-layer 136 deposited on the side wall 132. Depending upon thesealing process used in the fabrication, the hermetic sealing-layer 136for sealing the sealable opening 135 can be a metal layer or an oxidelayer.

When each of the sealable opening 135 in the side wall 132 is sealedwith the hermetic sealing-layer 136, a hermetically sealed empty spacecan be formed with the combination of the inner space 138 of eachchamber 130 and the other three empty spaces (e.g., the first emptyspace 161, the second empty space 162, the third empty space 163). Thishermetically sealed empty space is hermetically sealed by thecombination of the hermetic sealing-layer 136, the first seal structure141, the second seal structure 142, and the third seal structure 143. Insome embodiments, the combined empty space formed with the combinationof the inner space 138 of each chamber 130 and the other three emptyspaces (e.g., the first empty space 161, the second empty space 162, thethird empty space 163) can be first brought into equilibrium with apredetermined air pressure in a vacuum space; then, each of the sealableopenings 135 in the side wall 132 is sealed with the hermeticsealing-layer 136 while some vacuum (e.g., with a pressure ranging from10⁻⁹ to 10⁻³ torr) is maintained at the environment. After each of thesealable openings 135 is sealed in the vacuum maintained, each of thefirst empty space 161, the second empty space 162, and the third emptyspace 163 becomes vacuum space with its pressure lower than apredetermined value. In some embodiments, the residual pressure of thisvacuum space can be in the range from 10⁻⁹ to 10⁻³ torr. After thehermetic sealing of the sealable openings 135, no particles and vaporcan get into the sealed empty space; consequently, and the influence ofthe stiction effects on the performance of the MEMS microphone 100 isreduced.

In FIG. 2 , the first diaphragm 101 and the second diaphragm 102 areboth deformable when sound waves exert pressure on the first diaphragm101 through an opening 45 in the substrate 40. Under the pressure causedby the sound waves, the first diaphragm 101 can bend towards or awayfrom the first backplate 111. Because the second diaphragm 102 isjointed with the first diaphragm 101 at multiple locations by pillars120, when the first diaphragm 101 bends towards or away from the firstbackplate 111, the second diaphragm 102 bends towards or away from thesecond backplate 112 in synchronization. Because such synchronization,the total change of the capacitance value due to the sound waves can beenhanced, for example, by connecting in parallel a first capacitorelement (formed between the first diaphragm 101 and the first backplate111) with a second capacitor element (formed between the seconddiaphragm 102 and the second backplate 112).

For example, in FIG. 2 , electrical contacts 82 and 84 can berespectively connected to the first diaphragm 101 and backplate 111 toform the two terminals of the first capacitive element; electricalcontacts 86 and 88 can be respectively connected to the second diaphragm102 and the second backplate 112 to form the two terminals of the secondcapacitive element. The first capacitive element and the secondcapacitive element can be connected in parallel by connecting theelectrical contact 82 with the electrical contact 86 to form a firstcombined terminal and by connecting the electrical contact 84 with theelectrical contact 88 to form a second combined terminal. Thecapacitance change between the first combined terminal and the secondcombined terminal will be the sum of the capacitance change of the firstcapacitive element and the capacitance change of the second capacitiveelement.

In FIG. 2 , there are multiple air holes 155 located at places outsidethe boundaries defining the first empty space 161, the second emptyspace 162, and the third empty space 163. The multiple air holes 155 areimplemented to balance a first pressure at one side of the microphone100 (e.g., the side near the opening 45) with a second pressure at theother side of the microphone 100 (e.g., the side near the secondbackplate 112). Such balancing of the two pressures can decrease thechance of breaking the diaphragms 101 and 102 when a large air pressureis present at a location near the opening 45 of the microphone 100. Eachof the air holes 155 passes the first diaphragm 101, the first backplate111, the second diaphragm 102, and the second backplate 112,respectively through an open hole 155A, an open hole 155B, an open hole155C, and an open hole 155D. In some embodiments, open holes 155A, openholes 155B, open holes 155C, and open holes 155D—which are shown in FIG.3A, FIG. 3B, FIG. 3C, and FIG. 3D respectively—are distributed evenlynear the circumference of a circle.

In FIG. 3A, in addition to the open holes 155A, locations 120A thatindicate where the end of one of the pillars 120 joints the firstdiaphragm 101 are also shown, in accordance with some embodiments. InFIG. 3B, in addition to the open holes 155B, accommodating-openings 115that allow the pillars 120 to pass through the first backplate 111 arealso shown, in accordance with some embodiments. In FIG. 3C, in additionto the open holes 155C, locations 120C that indicate where the end ofone of the pillars 120 joints the second diaphragm 102 are also shown,in accordance with some embodiments. The locations of the multipleopenings 105 in the second diaphragm 102 have not been shown in FIG. 3C.In FIG. 3D, in addition to the open holes 155D, the layout of the ventholes 125 in the second backplate 112 are also shown, in accordance withsome embodiments. Each of the vent holes 125 forms an airconnection—through the second backplate 112—between the third emptyspace 163 and the inner space 138 of one of the chambers 130. In FIG.3E, an alternative layout of the vent holes 125 in the second backplate112 are illustrated, in accordance with some embodiments.

In the embodiments as shown in FIGS. 3A-3D, the open holes (e.g., 155A,155B, 155C, and 155D), the accommodating-openings 115 for passing thepillars, and the ends of the pillars (e.g., 120A and 120D) are all inthe shape of a circle; in other embodiments, they can be in othergeometric shapes. When a pillar 120 is in the form of a cylinder, thediameter of the circle surrounding the accommodating-opening 115 islarger than the diameter of the circle surrounding the cross-section ofthis pillar 120.

FIG. 4 , FIGS. 5A-5D, and FIGS. 6A-6D are cross-section views of devicestructures for showing methods of manufacturing a MEMS microphone 100that has dual diaphragms in accordance with some embodiments.

FIG. 4 is a cross-section view of a device structure 190 that is anintermediate product created during the process of manufacturing theMEMS microphone 100 in accordance with some embodiments. The devicestructure 190 includes a substrate 40, a first diaphragm 101, a seconddiaphragm 102, a first backplate 111, and a second backplate 112. Thefirst diaphragm 101 is supported by the substrate 40. In the embodimentas shown in FIG. 4 , the first diaphragm 101 is formed in a firstconducting layer deposited on a base oxide layer 70 supported by thesubstrate. In some embodiments, the first diaphragm 101 can be formed ina first conducting layer deposited on the substrate without the baseoxide layer 70. The first backplate 111, with multipleaccommodating-openings 115, is separated from the first diaphragm 101 bya first layer of oxide material 71.

The second diaphragm 102 is separated from the first backplate 111 by asecond layer of oxide material 72. The first backplate 111 is locatedbetween the first diaphragm 101 and the second diaphragm 102. The seconddiaphragm 102 joints the first diaphragm together at multiple locationsby pillars 120 through the accommodating-openings 115 in the firstbackplate 111. The second backplate 112, with vent hole 125, isseparated from the second diaphragm 102 by a third layer of oxidematerial 73. The second diaphragm 102 is located between the firstbackplate 111 and the second backplate 112. In general, anaccommodating-opening 115 is sufficiently larger than the cross-sectionof a pillar 120 to allow the pillar 120 move freely relative to thefirst backplate 111 along the direction perpendicular to the plane ofthe first backplate 111, after the oxides separating theaccommodating-opening 115 and the pillar 120 are removed in laterprocessing steps.

In FIG. 4 , multiple chamber precursor structures 130′ are located atone side of the second backplate 112. Each chamber precursor structure130′ in FIG. 4 is filled with oxide material and has one side alignedwith a vent hole 125 on the second backplate 112 and has the other sideformed by a side wall 132. The side wall 132, with two sealable openings135, is separated from the second backplate 112 by a fourth layer ofoxide material 74.

During the process of fabricating the device structure 190, the firstdiaphragm 101, the first backplate 111, the second diaphragm 102, andthe second backplate 112 are sequentially fabricated layer by layer,followed by the fabrication of the multiple chamber precursor structures130′. The first diaphragm 101, which is fabricated before thefabrication of other diaphragm and backplates, is formed in a firstconducting layer deposited on a base oxide layer 70 supported by asubstrate 40. In the next step, the first backplate 111, with multipleaccommodating-openings 115, is formed on a first oxide layer 71deposited on the first conducting layer that has the first diaphragm101. In some embodiments, before the first backplate 111 is formed, thefirst seal structure 141 can be formed, at a first boundary enclosingthe first empty space 161, between the first diaphragm 101 and the firstbackplate 111. In one example, the first seal structure 141 can beformed by depositing needed material in an opening trench, formed in thefirst oxide layer 71, along the first boundary enclosing an oxide filledvolume space for creating the first empty space 161.

In the next step, a second diaphragm 102 is formed in a secondconducting layer on a second oxide layer 72 deposited on the firstbackplate 111, with the second diaphragm 102 jointing the firstdiaphragm 101 together at multiple locations by pillars 120 through theaccommodating-openings 115 in the first backplate 111. In someembodiments, before the second diaphragm 102 is formed, the second sealstructure 142 can be formed at a second boundary enclosing an oxidefilled volume space for creating the second empty space 162 between thesecond diaphragm 102 and the first backplate 111. In one example, thesecond seal structure 142 can be formed by depositing needed material inan opening trench, formed in the second oxide layer 72, along the secondboundary enclosing the oxide filled volume space for creating the secondempty space 162.

In the next step, a second backplate 112, with the vent holes 125, isformed on a third oxide layer 73 deposited on the second conductinglayer that has the second diaphragm 102. In some embodiments, beforesecond backplate 112 is formed, a third seal structure 143 can beformed, at a third boundary enclosing an oxide filled volume space forcreating the third empty space 163 between the second diaphragm 102 andthe second backplate 112. In one example, the third seal structure 143can be formed by depositing needed material in an opening trench andformed in the third oxide layer 73, along the third boundary enclosingthe oxide filled volume space for creating the third empty space 163.

In the next step, multiple chamber precursor structures 130′ are formed.Each one of the multiple chamber precursor structures 130′ has one sidealigned with a vent hole 125 in the second backplate 112. In the processof forming the multiple chamber precursor structures 130′, a side wall132 for each chamber precursor structure 130′ is formed on a fourthoxide layer 74 deposited on the second backplate 112. In one embodimentas shown in FIG. 4 , the side wall 132 has two sealable openings 135. Insome embodiments, before the side wall 132 is formed for the chamberprecursor structure 130′, the other walls for the chamber precursorstructure 130′ (which encloses the chamber precursor structure 130′byconnecting the side wall 132 with the second backplate 112) can beformed by depositing needed material in an opening trench formed in thefourth oxide layer 74.

During the process of fabricating the device structure 190, variousmicro-fabrication techniques are used. In some embodiments, layers ofmaterials for fabricating the device structure 190 can be formed by adeposition process, such as, chemical vapor deposition (CVD), physicalvapor deposition (PVD), or atomic layer deposition (ALD). For example, adeposition process can be used for forming a layer of material forfabricating a diaphragm (e.g., 101 and 102), a layer of material forfabricating a backplate (e.g., 111 or 112), a layer of material forfabricating various walls (e.g., 132) of the chamber precursorstructure, or a layer of oxides (e.g., 70, 71, 72, 73, or 74). In someembodiments, an oxide layer can be formed by a thermal process. Forexample, in FIG. 4 , the layer of base oxide 70 can be formed by placinga silicon substrate 40 in gases that is rich in oxygen (e.g., oxygen gasmixed with argon gas) in an elevated temperature; other layer of oxides(e.g., 71, 72, 73, or 74) can be formed by thermally oxidizing a layerof previously deposited polysilicon.

In FIG. 4 , each of the first diaphragm 101, the first backplate 111,the second diaphragm 102, and the second backplate 112 can be formed inan etching process according to designed patterns in a mask layer. Insome embodiments, the mask layer can be photoresist or a nitride (e.g.,Si3N4) patterned using a photolithography process. In some embodiments,the etching process can be a dry etching process, for example, using adry etchant that has an etching chemistry comprising a fluorine species(e.g., CF4, CHF3, C4F8). During the process of fabricating the devicestructure 190, various patterned oxide layers need to be formed in theoxide layer 70, 71, 72, 73, or 74; these patterned oxide layers can bealso formed in an etching process using a wet etchant.

In some embodiments for fabricating the device structure 190, each ofthe first diaphragm 101 and the second diaphragm 102 can be formed in alayer of polysilicon. In some embodiments, when the first diaphragm 101is formed, the open holes 155A and the structures for electricalcontacts (e.g., 81 and 82) are formed in the same layer of polysilicon.In some embodiments, when the second diaphragm 102 having openings 105is formed, the open holes 155C and the structures for electricalcontacts (e.g., 81, 82, 84, and 86) are formed in the same layer ofpolysilicon.

In some embodiments, each of the first backplate 111 and the secondbackplate 112 can be formed in a layer of polysilicon. In someembodiments, each of the first backplate 111 and the second backplate112 can be formed in a layer of polysilicon sandwiched between twolayers of silicon nitride. In some embodiments, when the first backplate111 having accommodating-openings 115 is formed, the open holes 155B andthe structures for electrical contacts (e.g., 81, 82, and 84) are formedin the same layer. In some embodiments, when the second backplate 112having vent holes 125 is formed, the open holes 155D and the structuresfor electrical contacts (e.g., 81, 82, 84, 86, and 88) are formed in thesame layer.

In some embodiments, each layer of oxides (e.g., 70, 71, 72, 73, or 74)can be a layer of silicon oxide. In some embodiments, when the layer ofbase oxide 70 is patterned, via holes for electrical contacts (e.g., 81)are formed in the same layer. In some embodiments, when the first oxidelayer 71 is patterned, the needed openings for fabricating pillars 120,the needed opening trenches for fabricating the first seal structure141, and the via holes for electrical contacts (e.g., 81 and 82) areformed in the same layer. In some embodiments, when the second oxidelayer 72 is patterned, the needed openings for fabricating pillars 120,the needed opening trenches for fabricating the second seal structure142, and the via holes for electrical contacts (e.g., 81, 82, and 84)are formed in the same layer. In some embodiments, when the third oxidelayer 73 is patterned, the needed opening trenches for fabricating thethird seal structure 143 and the via holes for electrical contacts(e.g., 81, 82, 84, and 86) are formed in the same layer of siliconoxide.

In some embodiments, when the fourth oxide layer 74 is patterned, theneeded opening trenches for fabricating the walls to enclose the chamberprecursor structures 130′ are formed in the fourth oxide layer 74; then,the walls to enclose the chambers 130 is fabricated in these openingtrenches in the fourth oxide layer 74, and the side walls 132 havingsealable openings 135 are fabricated in a layer of material on thefourth oxide layer 74. In some embodiments, the walls to enclose thechamber precursor structures 130′ by depositing poly-silicon into theopening trenches in the fourth oxide layer 74; the side walls 132 can beformed by depositing poly-silicon on the fourth oxide layer 74, andfollowed by a patterning process.

FIGS. 5A-5D are cross-section views of device structures for showing onemethod of manufacturing a MEMS microphone 100 that has dual diaphragmsin accordance with some embodiments. With this manufacturing method, thesealable openings 135 in the side wall 132 for a chamber 130 as shown inFIG. 4 are hermetically sealed with an oxide layer.

As shown in FIG. 5A, after the device structure 190 as shown in FIG. 4is fabricated, a first protection mask 171 is formed to expose sealableopenings 135 for an etching process while protecting other parts of thefourth oxide layer 74. In one embodiment, the first protection mask 171is formed by creating predetermined patterns in a photoresist layer.Next, the device structure 190 is immersed in a wet etchant to removeoxide materials in parts of some oxide layers (e.g. 74, 73, 72, and 71)to form the inner space 138 (see FIG. 5B) and the empty spaces (e.g.,163, 162, 161). The wet etch also removes oxide materials from thechamber precursor structures 130′ to provide chambers 130. Examples ofthe wet etchant that can be used for removing these oxide materialsinclude hydrofluoric acid (HF), Buffered Oxide Etch (BOE) solution (6parts 40% NH4F and 1 part 49% HF), or Tetramethylammonium hydroxide(TMAH).

In the next step, as shown in FIG. 5B, after the first protection mask171 is removed (e.g., by stripping off the photoresist), a fifth oxidelayer 75 is deposited on the fourth oxide layer 74 and on the side walls132 to hermetically seal off the sealable openings 135 in the side wall132. Then, the via holes 182, 184, 186, 188, and 181 respectively forelectrical contacts 82, 84, 86, 88, and 81 are made in the fifth oxidelayer 75 and the fourth oxide layer 74, before these electrical contactsare made by depositing and patterning one or more metal layers on thefifth oxide layer 75. In some embodiments, during the process forhermetically sealing off the sealable openings 135, the fifth oxidelayer 75 can be deposited on the fourth oxide layer 74 and on the sidewalls 132 while the device structure 190 is maintained in a vacuum space(e.g., with a pressure ranging from 10⁻⁹ to 10⁻³ torr).

In the next step, as shown in FIG. 5C, a second protection mask 172(e.g., in a photoresist layer) is formed on the fifth oxide layer 75 toopen up parts of the fifth oxide layer 75 for forming the air holes 155in an etching process. In this etching process, the device structure 190is immersed in a wet etchant to remove some oxide materials in selectedparts of the oxide layers 75, 74, 73, 72, 71, and 70. These removedoxide materials, as shown in FIG. 6C, include materials in the fifthoxide layer 75 covering the open hole 155D, in the fourth oxide layer 74covering the open hole 155D, in the third oxide layer 73 between theopen hole 155D and the open hole 155C, in the second oxide layer 72between the open hole 155C and the open hole 155B, in the first oxidelayer 71 between the open hole 155B and the open hole 155A, and in thebase oxide layer 70 covering the open hole 155A.

In FIG. 5C, a third protection mask 173 (e.g. in a photoresist layer) isformed on the substrate 40 to open up selected parts of the substrate 40for an etching process. Then, the substrate 40 is etched according tothis third protection mask 173 to create an opening 45 in the substrate40. In some embodiments, the opening 45 in the substrate 40 can becreated by anisotropic plasma etching. In some embodiments, before thethird protection mask 173 is formed on the substrate 40, the substrate40 can be grinded to a predetermined thickness. In some embodiments, thepredetermined thickness can be in the range from 20 μm to 400 μm.

In the next step, as shown in FIG. 5D, after removing the secondprotection mask 172 and the third protection mask 173, the MEMSmicrophone 100 having dual diaphragm is fabricated.

FIGS. 6A-6D are cross-section views of device structures for showinganother method of manufacturing a MEMS microphone 100 that has dualdiaphragms in accordance with some embodiments. With this manufacturingmethod, the sealable openings 135 in the side wall 132 for the chamberprecursor structure 130′ as shown in FIG. 4 are hermetically sealed witha metal layer.

As shown in FIG. 6A, after the device structure 190 as shown in FIG. 4is fabricated, a first protection mask 171 (e.g., in a photoresistlayer) is formed to expose sealable openings 135 for an etching processwhile protecting other parts of the fourth oxide layer 74. Next, thedevice structure 190 is immersed in a wet etchant to remove oxidematerials in parts of some oxide layers (e.g. 74, 73, 72, and 71) toform the inner space 138 (see FIG. 6B) and the empty spaces (e.g., 163,162, 161). The wet etch also removes oxide materials from the chamberprecursor structures 130′ to provide chambers 130. In one embodiment,before the first protection mask 171 is formed as shown in FIG. 6A, thevia holes 182, 184, 186, 188, and 181 respectively for electricalcontacts 82, 84, 86, 88, and 81 are made in the fourth oxide layer 74.

In the next step, as shown in FIG. 6B, after the first protection mask171 is removed (e.g., by stripping off the photoresist), a metal layer175 is deposited on the side walls 132 to hermetically seal off thesealable openings 135 in the side wall 132, while the device structure190 is maintained in a vacuum space (e.g., with a pressure ranging from10⁻⁹ to 10⁻³ torr). In some embodiments, when the metal layer 175 isdeposited on the side walls 132, the metal layer 175 is also depositedon the fourth oxide layer 74 in the same step, to form the electricalcontacts 82, 84, 86, 88, and 81 respectively through the via holes 182,184, 186, 188, and 181. In some other embodiments, the electricalcontacts 82, 84, 86, 88, and 81 can be made in a separate step, bydepositing and patterning a metal layer, on the fourth oxide layer 74,that is different from the metal layer 175.

In the next step, as shown in FIG. 6C, a second protection mask 172(e.g. in a photoresist layer) is formed on the fourth oxide layer 74 toopen up parts of the fourth oxide layer 74 for forming the air holes 155in an etching process. In this etching process, the device structure 190is immersed in a wet etchant to remove some oxide materials in selectedparts of the oxide layers 74, 73, 72, 71, and 70, as shown in FIG. 6C.

In FIG. 6C, a third protection mask 173 (e.g. in a photoresist layer) isformed on the substrate 40 to open up selected parts of the substrate 40for an etching process. Then, the substrate 40 is etched according tothis third protection mask 173 to create an opening 45 in the substrate40. In some embodiments, before the third protection mask 173 is formedon the substrate 40, the substrate 40 can be grinded to a predeterminedthickness.

In the next step, as shown in FIG. 6D, after removing the secondprotection mask 172 and the third protection mask 173, the MEMSmicrophone 100 having dual diaphragm is fabricated.

Some aspects of the present disclosure relate to a microphone. Themicrophone includes a substrate having an opening, a first diaphragm, afirst backplate, a second diaphragm, and a second backplate. The firstdiaphragm faces the opening in the substrate. The first backplateincludes multiple accommodating-openings and it is spaced apart from thefirst diaphragm. The second diaphragm joints the first diaphragmtogether at multiple locations by pillars passing through theaccommodating-openings in the first backplate. The first backplate islocated between the first diaphragm and the second diaphragm. The secondbackplate includes at least one vent hole and it is spaced apart fromthe second diaphragm. The second diaphragm is located between the firstbackplate and the second backplate.

Other aspects of the present disclosure relate to a method ofmanufacturing a microphone. An intermediate device structure isfabricated. The intermediate device structure includes a first diaphragmsupported by a substrate, a first backplate, a second diaphragm, asecond backplate, and multiple chambers. The first backplate includesmultiple accommodating-openings and it is separated from the firstdiaphragm by a first layer of oxide material, and a second backplate.The second diaphragm is separated from the first backplate by a secondlayer of oxide material and it joints the first diaphragm together atmultiple locations by pillars passing through the accommodating-openingsin the first backplate. The first backplate is located between the firstdiaphragm and the second diaphragm. The second backplate includes atleast one vent hole and it is separated from the second diaphragm by athird layer of oxide material. The second diaphragm is located betweenthe first backplate and the second backplate. Each of multiple chambershas one side aligned with the at least one vent hole in the secondbackplate and has the other side formed by a side wall having twosealable openings. The side wall is separated from the second backplateby a fourth layer of oxide material. In the method, after theintermediate device structure is fabricated, a first protection mask iscreated on the fourth layer of oxide material. The first protection maskexposes the two sealable openings in the side wall for each of themultiple chamber precursor structures. Parts of multiple layers of oxidematerial are etched to form a first empty space between the firstdiaphragm and the first backplate, a second empty space between thesecond diaphragm and the first backplate, and a third empty spacebetween the second diaphragm and the second backplate, and an innerspace in each chamber created from each of the multiple chamberprecursor structures. The multiple layers of oxide material includes thefourth layer of oxide material, the third layer of oxide material, thesecond layer of oxide material, and the first layer of oxide material.

Other aspects of the present disclosure relate to a method ofmanufacturing a microphone. A first diaphragm is formed in a firstconducting layer deposited on a base oxide layer supported by asubstrate. A first backplate having multiple accommodating-openingstherein is formed, and the first backplate is on a first oxide layerdeposited on the first conducting layer. A second diaphragm is formed ina second conducting layer on a second oxide layer deposited on the firstbackplate, with the second diaphragm jointing the first diaphragmtogether at multiple locations by pillars passing through theaccommodating-openings in the first backplate. A second backplate havingat least one vent hole therein is formed, and the second backplate is ona third oxide layer deposited on the second conducting layer. A sidewall having two sealable openings is formed for each one of multiplechambers, and the side wall is on a fourth oxide layer deposited on thesecond backplate. Each one of the multiple chambers has another sidealigned with a vent hole in the second backplate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A micro-electrical-mechanical-system (MEMS) device, comprising: a substrate having an opening; a first diaphragm facing the opening in the substrate; a first backplate including multiple accommodating-openings and spaced apart from the first diaphragm; a second diaphragm jointing the first diaphragm together at multiple locations by pillars through the accommodating-openings in the first backplate, with the first backplate located between the first diaphragm and the second diaphragm; and a first seal structure jointing the first diaphragm and the first backplate at a first boundary enclosing a first empty space between the first diaphragm and the first backplate; and wherein the first seal structure includes a hermetic sealing-layer disposed on a side wall surface that is perpendicular to the first diaphragm.
 2. The MEMS device of claim 1, wherein the hermetic sealing-layer is a metal layer.
 3. The MEMS device of claim 1, wherein the hermetic sealing-layer is an oxide layer.
 4. The MEMS device of claim 1, further comprising: a second seal structure jointing the second diaphragm and the first backplate at a second boundary enclosing a second empty space between the second diaphragm and the first backplate.
 5. The MEMS device of claim 1, further comprising: a second backplate including at least one vent hole and spaced apart from the second diaphragm, with the second diaphragm located between the first backplate and the second backplate.
 6. The MEMS device of claim 5, further comprising: a third seal structure jointing the second diaphragm and the second backplate at a third boundary enclosing a third empty space between the second diaphragm and the second backplate.
 7. A micro-electrical-mechanical-system (MEMS) device, comprising: a substrate having an opening; a first diaphragm facing the opening in the substrate; a first backplate including multiple accommodating-openings and spaced apart from the first diaphragm; a second diaphragm jointing the first diaphragm together at multiple locations by pillars through the accommodating-openings in the first backplate, with the first backplate located between the first diaphragm and the second diaphragm; a seal structure jointing the second diaphragm and the first backplate at a boundary enclosing an empty space between the second diaphragm and the first backplate; and a second backplate including at least one vent hole and spaced apart from the second diaphragm, with the second diaphragm located between the first backplate and the second backplate.
 8. The MEMS device of claim 7, further comprising: a second seal structure jointing the first diaphragm and the first backplate at a second boundary enclosing a second empty space between the first diaphragm and the first backplate.
 9. The MEMS device of claim 7, further comprising: a third seal structure jointing the second diaphragm and the second backplate at a third boundary enclosing a third empty space between the second diaphragm and the second backplate.
 10. A micro-electrical-mechanical-system (MEMS) device comprising: a substrate having an opening; a first diaphragm facing the opening in the substrate; a second diaphragm jointing the first diaphragm together at multiple locations by pillars; a backplate including at least one vent hole and spaced apart from the second diaphragm, with the second diaphragm located between the first diaphragm and the backplate; a seal structure jointing the second diaphragm and the backplate at a boundary enclosing an empty space between the second diaphragm and the backplate; and multiple chambers located at one side of the backplate, wherein at least one of the multiple chambers has an inner space thereof connecting to the empty space at another side of the backplate through the at least one vent hole in the backplate.
 11. The MEMS device of claim 10, further comprising: a second seal structure jointing the first diaphragm and the backplate at a second boundary enclosing a second empty space between the first diaphragm and the backplate.
 12. The MEMS device of claim 11, further comprising: a third seal structure jointing the second diaphragm and the backplate at a third boundary enclosing a third empty space between the second diaphragm and the backplate.
 13. The MEMS device of claim 10, wherein the at least one of the multiple chambers further comprises: a side wall spaced apart from the backplate; and a sealable opening in the side wall.
 14. The MEMS device of claim 13, wherein the sealable opening is sealed with a hermetic sealing-layer deposited on the side wall.
 15. The MEMS device of claim 14, wherein the hermetic sealing-layer is a metal layer.
 16. The MEMS device of claim 14, wherein the hermetic sealing-layer is an oxide layer.
 17. The MEMS device of claim 10, further comprising: a second backplate including multiple accommodating-openings and spaced apart from the second diaphragm, wherein the pillars extend through the multiple accommodating-openings, respectively, in the second backplate, with the second backplate located between the first diaphragm and the second diaphragm.
 18. The MEMS device of claim 5, further comprising: multiple chambers located at one side of the first backplate, wherein at least one of the multiple chambers has an inner space thereof connecting to an empty space at another side of the first backplate through the at least one vent hole.
 19. The MEMS device of claim 7, wherein the seal structure includes a hermetic sealing-layer deposited on a side wall surface that is perpendicular to the first diaphragm.
 20. The MEMS device of claim 10, wherein the seal structure includes a hermetic sealing-layer deposited on a side wall surface that is perpendicular to the first diaphragm. 